The U.S. State Department says it is "profoundly disappointed" in the Republic of Congo's election, which allowed President Denis Sassou Nguesso to extend his 32 years in power.

Spokesman Mark Toner said in a statement that widespread irregularities during the election and arrests of opposition supporters afterward marred what was otherwise a peaceful vote.

He said the U.S. is also "deeply concerned about the welfare of thousands of Congolese who awoke on April 4 to the sound of gunfire and explosions and fled their homes" in the capital city, Brazzaville.

The Congolese government says former members of a disbanded militia attacked government targets that day. It says three security officers, two civilians, and 12 assailants were killed in the clashes.

Opposition candidates say the March 20 poll was rigged to favor Nguesso. One candidate, General Jean-Marie Mokoko, called for civil disobedience to protest the official results.

Second-place candidate Guy-Brice Parfait Kolelas conceded defeat Thursday, saying he wants to avoid further violence, but maintained the polling was unfair. He also blamed the government for the attacks, saying they were a set-up to avoid protests.

Supporters of Guy Brice Parfait Kolelas, the Interim President of the Congolese Movement for Democracy and Integral Development demonstrate at the candidate head quarter in Brazzaville on March 23, 2016.

Sassou Nguesso ran for re-election after pushing through constitutional changes to remove age and term limits.

The 72-year-old president has ruled the Republic of Congo for all but five years since 1979.

He won elections in 2002 and 2009 that were disputed by the opposition.